Individual differences in complex cognitive tasks like reading comprehension have been shown to be related to individual differences on the number of items that can be retained for a short period of time in a memory span task that requires processing as well as storage of the span items. The goal of this research is to determine whether this working memory limitation plays a causal role in the higher level cognitive tasks or whether a third factor, unrelated to the amount of total processing available to the individual, accounts for this relationship. The first question posed by the research is whether the relationship between working memory and comprehension occurs because of a trade off between the time to perform mental operations and the amount of available storage capacity. College age subjects perform a dual processing-storage task in which they will solve arithmetic strings and try to recall words or letters presented after each arithmetic string. The time to present the elements of the task, the time to solve the arithmetic problem and the time to encode the to-be-recalled items will be measured and used to operationalize the trade off between processing time and storage. A second question asks whether the difficulty of the processing component of the span task the span-comprehension relationship and the measure of working memory capacity over age. Two of the research questions concern the role of working memory in children, specifically: (1) whether what we refer to here as working memory is the same construct as that measured by M-Space tasks in the developmental literature and (2) whether individual differences in working memory can be used to predict how well a child would learn to read in the first grade and whether the individual differences in working memory observed in pre-school persist over a 3 year period and predict differences in the performance on academic skills over the early school years. We will also be concerned about whether the working memory measured by the tasks used here represents a unitary, limited capacity structure or whether there might be different working memories for verbal and spatial domains. The last research question is whether there is a relationship between speed of mental processing and working memory capacity. This question will be addressed both at developmental and individual differences in working memory capacity. While the work does not deal specifically with the underlying neuroscience of capacity limitations, the studies should lead to a better understanding of the nature of working memory and its relationship to higher level cognition. If working memory plays a causal role in such important everyday tasks as reading, it likely would play a role in the loss of cognitive function as a result of brain trauma.